Switching devices for switching electric currents typically comprise at least one contact system and further housing modifications. The contact system comprises an electric switch and serves to switch electric currents. A class of switching devices are the so-called “circuit breakers”, which can typically switch currents of 100A or more.
These circuit breakers comprise a housing, in which the individual phases of the currents are switched. The individual phases of the currents can be accommodated in pole cartridges, which are enclosed by a dedicated housing. Moving and fixed contacts are accommodated in the pole cartridges, which moving and fixed contacts can be mechanically separated or brought together so as to switch off or on the currents. During separation of the moving and fixed contacts of a pole cartridge, an arc, which is typically quenched in a so-called “quenching chamber”, is formed. Likewise, circuit breakers are known which do not contain any pole cartridges and which accommodate moving and fixed contacts in their housing.
In circuit breakers, it is necessary in order to achieve good current limitation to quickly build up a high arc voltage. This is achieved with so-called “double-break interrupters”, which split the switching path twice and thus produce simultaneously two arcs in the event of a short circuit. The arc voltage produced by the arc is now present twice in the same time unit, which improves the current limitation in comparison with single-break interruption systems. Typically, in the case of so-called “double-break interrupters”, two electrical contacts are arranged on a rotatably mounted contact link, which contacts represent the moving contacts. The two moving contacts interact with two fixed contacts of the electric switch so as to close or open the circuit.
DE 692 09 972 T2 describes a circuit breaker comprising single-pole units. In the case of this circuit breaker, the contact link of each pole cartridge is fitted in freely suspended fashion in a breaker shaft section, and the rigid mechanical connection between the individual breaker shaft sections is provided by two rods arranged parallel to the breaker shaft and eccentrically with respect to the rotary spindle thereof. This design ensures the application of the contact force, dynamic contact opening in the event of a short circuit of the electric switch and coupling to a switching mechanism for opening and closing the electric switch with an actuating lever.
DE 693 04 374 T2 discloses a circuit breaker comprising a mold housing with delay at the movement end of the contact link repulsion. The contact link is mounted without a spindle in the rotor housing. For this, the contact link comprises tension springs, which serve the purpose of ensuring, in the switch-on position of the circuit breaker, a force pressure exerted by the contact link on the stationary contacts and, at the same time, enable a rotation of the contact link under the action of the electrodynamic forces in the direction of the repulsion/switch-off position.
Double-break contact systems having a rotary design are very often susceptible to asymmetries. The asymmetries may be due to the tolerance zone position of the component parts or to the asymmetrical erosion during operation. For example, the contact pieces of the contact link can erode asymmetrically. These asymmetries result in uneven contact forces and contact resistances at the contact points. Previously known possible solutions for avoiding these asymmetries provide a possible way of compensation by virtue of the movable contact link and by virtue of a floating arrangement of the breaker shaft or the rotor in the pole cartridge.